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Laying a wooden deck on slab and joists

Wooden deck boards are available in different species and colors. They allow a multitude of styles. A concrete slab is here the basis of the installation. It must be flat, with a slight slope to allow the evacuation of water in case of rain. If you want to install a terrace with an area greater than 20 m2 and a height greater than 60 cm, you must apply for a work permit from the town hall, or even a building permit. The joist thickness must be at least 20 mm to ensure good air circulation. Their width must be 45 mm minimum to allow juxtaposing two blades.

Necessary material

  • Cales
  • square
  • Metre
  • Pencil
  • Mason Rule
  • Bubble level
  • Hand saw
  • Circular saw
  • Hammer drill
  • Strawberry
  • Hammer
  • screwdriver
  • 5 mm thick plastic profile
  • Rope
  • Servant

Steps

  1. Laying the joists of the terrace
  2. Cutting the first terrace boards
  3. Fabrication of a drilling template
  4. Laying the following blades
  5. Laying the edge blades

Laying the joists of the terrace

Joists in place

Joists in place

1. The realization of a wooden deck is always based on the same principle: an assembly of wooden boards is placed on a structure of joists or joists. At first, you will install the 2 end joists, to delimit the laying surface, perpendicular to the wall of your home. Put a first joist on your slab. In order to provide for the expansion of the wood, it is important to insert a shim 5 mm thick between the end of the joist and the wall. If the joist is too short: you need to saw another joist to complete the line. You must then measure the missing length and postpone this measurement on a joist. Draw a line at the square and saw with a hand saw. Now place this portion of joist in continuity with that already laid. If the joist is too long, you must saw it. You must then measure the excess length and postpone this measurement on the joist. Draw a line at the square and saw with a hand saw.

The first joists must be perpendicular to the wall

The first joists must be perpendicular to the wall

2. Now check with the square that the first joists are perfectly perpendicular to the wall. If your deck has to reach the edge of the slab, the joist must be aligned as much as possible with this edge.

Widen the pilot hole with a cutter so that the screw head does not protrude from the joists

Widen the pilot hole with a cutter so that the screw head does not protrude from the joists

3. Once the joists are positioned, you must attach them to the slab. Drill a pilot hole in the joist using a wood drill to the diameter of the dowel to be struck. Extend this pilot hole with a cutter so that the screw head does not protrude from the joist surface. Now drill the slab through the pilot hole with a concrete drill bit.

Place the dowels to hit

Place the dowels to hit

4. You must now place the dowels to hit. Using these dowels will make your job easier. Indeed, they include the screw and sink simply with the help of a hammer. The joists must be fastened every 70 cm or so at their ends. Once the joists are fixed, you can remove the shims.

Leave a gap of 40 cm maximum between each joist

Leave a gap of 40 cm maximum between each joist

5. You will now install the intermediate joists. For this installation, reproduce exactly the same process as for the reinforcement, respecting a spacing of 40 cm maximum between each joist.

Check the flatness of the joists at the bubble level

Check the flatness of the joists at the bubble level

6. Now check the flatness of all joists using a mason ruler and a bubble level. To do this, rest the mason rule, surmounted by the bubble level, across your structure. Reproduce this gesture in several places on the structure. Also check that all joists are perpendicular to the wall.

After fixing the joists remove the holds

After fixing the joists remove the holds

7. Now you have to fi x everything according to the previous method: drill the pilot holes, mill, drill the slab through the pilot holes, insert the dowels to hit and remove the shims.

Cutting the first terrace boards

Lay the first blade perpendicular to the joists

Lay the first blade perpendicular to the joists

1. The joists network is in place, you can start laying the blades. Lay the first blade perpendicular to the joists starting at an angle. Do not forget to put the holds.

Draw a cut mark on the blade

Draw a cut mark on the blade

2. The cut of the blade should arrive at mid-joist. You must draw a pencil mark on the blade. Place your blade on the workbench and draw the cut line square on the wrong side. Saw with a handsaw following the line. Reposition the blade on the joists.

Add 4 cm to the required length of the blade

Add 4 cm to the required length of the blade

3. You must now complete the first line by adding a blade portion. Measure the necessary length. Add 4 cm to this measurement, when cutting, to have an overhang at the end of the terrace. This overhang will be sawn at the end of installation for an impeccable finish.

Fabrication of a drilling template

Fabrication of the template for the location of the two holes

Fabrication of the template for the location of the two holes

1. To locate the location of the screws on the blade more easily, you will build a template. Take a blade drop of about 20 cm. Trace on this blade a straight line at a distance of half a joist width. Do the same at a distance of a quarter of joist. Locate on this second line the location of the two holes dividing them harmoniously across the width of the blade.

Drilling benchmarks of the template

Drilling benchmarks of the template

2. Now drill on these two marks. Your template is finished.

Fixing the first line of blades

Align the template in the middle of the joist

Align the template in the middle of the joist

1. Place the template precisely on the blade, aligning it in the middle of the joist. Drill pilot holes through the template taking care to only pierce the blade.

Remove the shim after screwing the pilot holes

Remove the shim after screwing the pilot holes

2. Mill the pilot holes and screw. You can now remove the hold. Repeat this process at each end of the line, garden side and wall side, then in the middle of the blades.

Laying the following blades

Do not forget to put a wedge at the end of the line

Do not forget to put a wedge at the end of the line

1. Your first line of blades is now laid. You can proceed with the installation of the following blades. Using a 5 mm thick plastic pro fi le you will provide a space for expansion between each line. As before, do not forget to put a shim at the end of the line.

Using the template to fix the blade

Using the template to fix the blade

2. Measure the portion of the blade to be cut so that it reaches mid-joist, mark this length on your blade with a pencil. With a square, trace your cut and saw the blade with the handsaw following this line. Lay this portion of the blade, then a whole blade to finish your line.

Laying a wooden deck on slab and joists: joists

3. Now fix the blades as before. Use your template to drill the pilot holes. Mill the pilot holes and screw. Secure the blades at the end of the line, at the junction of two blades and in the middle of the blade. Remove your cleat and plastic profile and continue attaching the following blades. Cover the entire surface of the terrace by following the same procedure: marking, sawing, pre-drilling using the template, milling, screwing, etc.

Laying the edge blades

Draw a chalk line from one side of the terrace to the other

Draw a chalk line from one side of the terrace to the other

1. You have finished laying the deck boards. You will be able to move to the end of the border. To ensure a perfect cut, you will use a chalk line. Stretch the chalk line from one end of the deck to the other at the edge of the joist. Pull the chalk up and let go. Your cutting line is now drawn on the ground.

Start sawing following the cut line

Start sawing following the cut line

2. You will be able to start sawing. Begin sawing with a hand saw and continue with the circular saw following the line of cut.

Laying a wooden deck on slab and joists: laying

3. You can now begin laying the edge blade that will hide the structure of your deck. Take a blade and back up the edge of the edge, minus 5 mm. It is necessary to provide a space of 5 mm between the ground and the edge of the blade, in order to let air and water circulate.

Laying a wooden deck on slab and joists: laying

4. Now draw the pencil line along the entire length of the blade. Saw with a circular saw following your line. To help you maintain the blade while cutting, you can use a maid.

Laying a wooden deck on slab and joists: joists

5. Now lay the edge blade against the edge of the deck. As for the deck boards, drill pilot holes, mill and then screw the edge blade into the joist. If the length of your blade is not enough, you need to add a portion of the blade. Measure the missing length, place this measurement on the blade and trace the line with a square. Saw with a handsaw, following the cut line and secure the missing portion in continuity with the already laid edge.

(photos / visuals: © Castorama, except special mention)

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Laying a wooden deck on slab and joists

FAQ - 💬

❓ Can you put decking on top of slabs?

👉 Leave the slabs alone if they have a good fall, tack 100mm or 150mm dpc on bottom edge of bearers, fold up the sides and tack/staple. Stick the decking on top. The decking will rot as quick as the bearers, plus rats love living under decking. Either put new slabs down or clean the existing.

❓ Can a deck be built over concrete?

👉 In most cases you can lay composite decking over concrete (keeping in mind you'll have to build a substructure that allows airflow and drainage).

❓ How do you build a raised deck on a concrete slab?

👉 Building a Deck over Concrete Step-By-Step

  1. Plan. deck footings over concrete. ...
  2. Create the footings. As I see it, here you have two options. ...
  3. Set Deck posts. ...
  4. Install the Deck Rim Joists (Outside Beams) ...
  5. Install Interior Joists. ...
  6. Install Blocking for extra stability. ...
  7. Install the Decking.

❓ Can I build a deck directly on the ground?

👉 Now here are your two options for laying your decking. You can either build it directly on the ground or square the site and build it on top of risers as a floating deck. If you lay it directly on the ground, you may find that it's more susceptible to absorbing moisture and might need additional maintenance.

❓ Can you put pressure treated wood directly on concrete?

👉 So, can you put pressure treated wood directly on concrete? Yes, you can.

❓ How do you install floor joists on a concrete slab?

👉 Install it flat on the slab surface, with the outside edge aligned against the side wall or the edge of the floor line. Secure each length to the slab with concrete nails spaced approximately 32 inches apart and 8 to 12 inches from each end. These will be the end "sill plates" that support the ends of the floor joists.

❓ Can you support a deck on a concrete slab?

👉 Putting a wooden deck surface over a concrete slab will allow the deck to stay stable without the usage of footings. By doing this, you're going to want to install sleepers, which are pieces of pressure-treated lumber, into the concrete so the deck has something to attach to.

❓ Do decks need footings?

👉 Large decks that are attached to the house should always have footings because they act to spread the heavy load of the deck from the surface of a support post over a large surface of the soil so the ground can adequately support it.

❓ What do you put under a deck?

👉 Put Gavel Under the Deck Washed gravel or crushed stone allows rain and snow to drain and create natural runoff. It also prevents weeds, protects against erosion, and keeps away moisture away from your deck's wooden substructure. Plan to buy enough gravel so that it's about 3-4″ deep.

❓ What should I put between wood and concrete?

👉 Anyplace where wood meets the ground or concrete, the lumber must be pressure treated. For additional moisture protection, a gasket or strip of closed-cell foam can be installed between the concrete foundation and the sill plate.

❓ Do I need a moisture barrier between concrete and wood?

👉 Moisture can destroy hardwood floors. It causes cupping, warping, and even mildew if not treated. You must install a moisture barrier to protect your flooring from water wicking up from below. Even with an epoxy coating over the concrete, it's best to lay down a waterproof membrane.

❓ How do you lay the boards on a deck?

👉 Now you’ve got the frame of your deck, you can lay the boards. Start in one corner of your sub-frame and position the first board across the inner joists so that the board runs in the opposite direction to the inner joists. If the joist runs horizontal, the boards should be vertical and vice versa.

❓ How much joist spacing do you need for synthetic decking?

👉 Some synthetic decking requires joist spacing at 12 in.; and if the deck is going to carry a heavy load, such as a hot tub, the joist spacing will often be reduced even more. For the deck shown here, we used standard 16-in.-o.c. joist spacing. Start the layout from the logical spot, which is not necessarily the deck’s edge.

❓ Can I Lay decking on top of a concrete slab?

👉 you dont need to worry about the dpc with decking. it is free draining and does not cause a problem as a patio would do. You can lay onto the concrete. do not put dpm under it as it will just hold the water. when we lay over concrete we use short legs of 4 x 2 to give support to the joists to stop them moving.

❓ Can you install stone deck tiles between deck joists?

👉 You can install stone deck tiles using a structural grate system in between the joists. Installing your decking at a 45-degree angle is a popular style for decks. This can be done to reduce decking seams or just for appearance. No; this is not a recommended practice.


Video Instruction: How To Build A Deck | #2 Framing [Beam/Joists/Ledger]